Generally, it is known that lubricants for refrigerator oils consist predominantly of highly refined mineral oils which have been dewaxed in excess of what is usual for lubricating oils in order to improve the flow properties at low temperatures.
Depending on the viscosity, usual pour-points for refrigerating machines are within a range of -50.degree. C. to -25.degree. C., and the low-temperature pour-points in accordance with DIN 51568 are within a range of -16.degree. C. to -38.degree. C. The temperature at which flocculation of the paraffin crystals occurs, which is important for the proper function of the lubricant, is likewise decreased by the additional dewaxing step.
The mineral oils suitable for the production of refrigerator oils are obtained by the known techniques through distillation of crudes and subsequent refining (Ullman Encyklopadie der technischen Chemie, 4th edition, vol.20, pp.484 et seq.). Depending on the origin of the raw material petroleum, so-called paraffin-base or naphthenic-base lubricating oils are obtained.
Paraffin-base lubricating oils comprise, predominantly, paraffinic molecules, while naphthenic-base ones comprise, predominantly, naphthenic or cycloparaffinic molecules respectively. Because of their superior properties at low temperatures, naphthenic-base oils are preferred for the production of refrigerator oils. Mineral oil-based refrigerator oils, in most cases, do not contain any additives.
In recent years, the technical advance in the field of refrigerating engineering has resulted in a continual increase of the requirements to be met by the lubricant and that both in respect of the low-temperature characteristics and of the thermal stability. In particular, elevated operating temperatures have caused premature fatigue of conventional refrigerator oils having no additional protection against aging so that premature replacement of such oils had be effected
The increased efficiency of modern refrigeration units also makes higher demands on the lubricating properties of a refrigerator oil in respect to the protection of frictionally engaged machine components from wear.
That is why there is a present need for improved lubricants for refrigerator systems. Thus, it is a primary object of the present invention to provide an improved lubricant for refrigerator systems and refrigerators.